Internal focusing wide angle eyepiece

ABSTRACT

A wide angle eyepiece for an internal focusing optical system of a viewing instrument comprises six elements. As viewed axially from rear to front, the eyepiece includes a biconvex doublet eyelens having a negative meniscus element and a biconvex element cemented together, a first positive meniscus single lens concaved toward the eye, a second positive meniscus single lens convexed toward the eye, and a positive meniscus doublet field lens having a biconvex element and a biconcave element cemented together. The field lens and at least one of the single lenses are axially movable together for focusing.

United States P Osawa et a1.

[ INTERNAL FOCUSING WIDE ANGLE EYEPIECE [75] Inventors: Kiyoynsu Osawa, Tokyo; Mutsuhiko Matsuura, Yokohama, both of Japan [73] Assignee: Nippon Kogaku K.K., Tokyo, Japan [22] Filed: June 12, 1972 [21] Appl. No.: 262,102

[30] Foreign Application Priority Data June 12,1971 Japan 46/41410 June 12, 1971 Japan 46/4141] [52] US. Cl. 350/220, 350/175 E [51] Int. Cl. G021) 25/00 [58] Field of Search 350/175 E, 220, 184

[56] References Cited UNITED STATES PATENTS 3,390,935 7/1968 Scidmore 350/175 E UX Oct. 30, 1973 2,859,654 11/1958 Back 350/184 3,202,050 8/1965 Seidenberg 350/175 E UX 3,410,629 11/1968 Carpenter et al 350/184 X 3,638,996 2/1972 Klein 350/175 E X Primary Examiner-John K. Corbin Att0rneyJoseph M. Fitzpatrick et a1.

[57] ABSTRACT A wide angle eyepiece for an internal focusing optical system of a viewing instrument comprises six elements. Asviewed axially from rear to front, the eyepiece includes a biconvex doublet eyelens having a negative meniscus element and a biconvex element cemented together, a first positive meniscus single lens concaved toward the eye, a second positive meniscus single lens convexed toward the eye, and a positive meniscus doublet field lens having a biconvex element and a biconcave element cemented together. The field lens and at least one of the single lenses are axially movable together for focusing.

3 Claims, 30 Drawing Figures Patented Oct. 30, 1973 3,768,890

FIG. IA FIG. EA

FIGJB FIG. 3B

FIG. lC FIG. 3C

Patented Oct. 30, 1973 7 3,768,890

7 Sheets-Sheet 4 FIG. 21 FIG. 2.] FIG. 2K

sPHEmc AL gm? ASTIGMATISM DISTORTION cowomow FCl C d d C F d C F d I I I i I [min I o I o su -20.0m o 20.0 -|o.0 0 10.0

g FIG. 2L AXIAL COMA FIELD TOTAL FIELD Patented Oct. 30, 1973 7 Sheets-Sheet 5 FIG. 48

FIG. 4C

FIG.4A

SPHERICAL ABERRATION SINE CONDITION dCF dC F 1mm u Fd Cd g mm G. d

AXIAL COMA i 36 d HALF- FIELD TOTAL FIELD Patented Oct. 30, 1973 3,768,890

7 Sheets-Sheet FIG. 4E FIG. 4F FIGAG SPHERICAL ABERRATION SINE ASTIGMATISM DISTORTION CONDITION Fd c d d c F d c F 1 a O -5.0 o 5.0 -2o.o o 20.0 |o.o o |o.0

COMA FIG. 4H

iAXIAL COMA d FIELD FIELD Patented Oct. 30, 1973 7 SheetsSheet FIG. 4d

FIG. 4K

FIG. 41

SPHERICAL ABERRATION SINE w 0 \i 00. 0 d o o a ll... 0 3 8 O 8 8 O m 3 2 2 6 2 F C I llrl I O F W m d O w M1 W W0 5 o m m COMA FIG. 4L

AXIAL COMA 1 INTERNAL FOCUSING WIDE ANGLE EYEPIECE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to oculars, and more particularly, to an internal focusing wide angle eyepiece usable with any device which requires an eyepiece, such as a telescope, binocular, measuring instrument, microscope, camera, cinecamera or the like.

2. Description of the Prior Art Heretofore, focusing by the use of an eyepiece or the adjustment of visibility to each individuals parallax has usually been accomplished by moving an entire eyepiece of a type already proposed. According to such practice, however, the viewers eye must follow the axial movement of the eyepiece. In other words, the viewer must move the position of his eye as the eyepiece is moved. Also, where air-tight or water-proof conditions are required in a mechanism, it has been very difficult to obtain complete integrity against water or air due to the mechanical provisions for axial movement of the eyepiece.

SUMMARY OF THE INVENTION We have conceived apparatus of the class described by which we are able to eliminate the above-noted disadvantages peculiar to the conventional eyepiece, and to provide an internal focusing wide angle eyepiece in which various aberrations are well corrected throughout a field of view as wide as 68 or more and which permits a relatively long distance from the first surface of a first lens element to the eye point (hereinafter referred to as eye distance), as viewed in the direction from the viewer's eye.

According to a broad feature of the present invention, there is provided a wide angle eyepiece for an internal focusing optical system of a viewing instrument which comprises, axially from rear to front, i.e., from the eye side to the object side, a biconvex doublet eyelens having a negative meniscus element and biconvex element cemented to each other, a first positive menis cus single lens concaved toward the eye, a second positive meniscus single lens convexed toward the eye, and a positive meniscus doublet field lens having a biconvex element and a biconcave element cemented to each other, the field lens and at least one of the single lenses being axially movable in unison for focusing According to another feature of the present invention there is provided awide angle eyepiece of the described type wherein the eyelens and the first positive meniscus single lens together form a stationary lens group and wherein the second single lens and the field lens together form a focusing lens movable for adjustment of visibility between negative, zero and positive diopter or for focusing from the infinite to a close distance.

According to still another feature of the present invention, there is provided a wide angle eyepiece of the described type wherein the eyelens forms a stationary lens group and wherein the first and second single lenses and the field lens together form a focusing lens movable for adjustment of visibility between negative, zero and positive diopter or for focusing from the infinite to the closest distance.

There has thus been outlined rather broadly the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto. Those skilled in the art will appreciate that the conception upon which this dis closure is based may readily be utlized as a basis for the designing of other structures for carrying out the several purposes of the invention. It is important, therefore, that the claims be regarded as including such equivalent construction as do not depart from the spirit and scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS A specific embodiment of the invention has been chosen for purposes of illustration and description, and is shown in the accompanying drawings, forming a part of the specification, wherein:

FIGS. l(A)l(C) schematically illustrate the arrangement of the wide angle eyepiece according to an embodiment of the present invention at stages of axial displacement of the focusing lens group corresponding to the negative, zero and positive diopter, respectively;

FIGS. 2(A)2(L) illustrate various aberrations in the arrangement of FIGS. 1(A)l(C) corresponding to the negative, zero and positive diopter, respectively;

FIGS. 3(A)(C) schematically illustrate the arrangement of wide angle eyepiece according to another embodiment of the present invention at stages of axial displacement of the focusing lens group corresponding to the negative, zero and positive diopter, respectively; and

FIGS. 4(A)4(L) illustrates various aberrations in the arrangement of FIGS. 3(A)-3(C) corresponding to the negative, zero and positive diopter, respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. l(A), the internal focusing wide angle eyepiece, according to an embodiment of the present invention, comprises six lens elements. As viewed from left to right, the eyepiece includes a first element Ll such as a negative meniscus lens convexed toward the eye or a plano-concave lens flattened toward the eye, a second element L2 such as a biconvex lens, a third element L3 such as a positive meniscus lens concaved toward the eye, a fourth element L4 such as a positive meniscus lens convexed toward the eye, a fifth element L5 such as a biconvex lens, and a sixth element L6 such as a biconcave lens. F is a focal plane of the entire eyepiece, and B.f is back focus. The first and second elements L1 and L2 and the fifth and sixth elements L5 and L6 are cemented together, respectively. When the diopter is zero, it is assumed that the total focal length of the entire eyepiece is f, the subtotal focal length of the first to third elements is f,, the subtotal focal length of the fourth to sixth elements if f the radii of curvature of the successive lens surfaces are R1, R2, etc., the center thicknesses or the interspatial distances of the successive elements are (1,, 11,, etc., the refractive indices of the respective elements for light having a wavelength of 5876A are m, n etc., and the Abbe numbers of the successive elements are etc. Then the arrangement shown satisfies the following conditions:

1.- With the lens group of the first to third elements stationary and with the focusing lens group of the fourth to sixth elements axially movable together within the range d l.lf, adjustment of the visibility can be made between negative, zero and positive diopter and focusing can be effected between infinity and the closest distance.

2. The sixth element L6 is a biconcave lens with a refractive index m, g n

3. f r 0.7f.

Regarding condition (1) above, it is natural with an angle eyepiece of the internal focusing type that the outer lens group thereof, i.e., the first to third elements adjacent the eye should be stationary while the inner lens group should be movable. According to the present embodiment, the inner lens group, comprising the fourth to sixth elements which are movable together, provides a focusing lens.

The upper limit d, l.lf of the condition that 05 l.lf is the limit of negative diopter (FIG. 1A), and the lower limit d, 0, i.e., the limit at which the fourth element L4 of the focusing lens group contacts the third element L3, is the limit of positive visibility (FIG. 1C). Between these two limits, the focusing lens may be freely moved and together with conditions (2) to (4), this maintains good characteristics of various aberrations such as spherical aberration, coma, astigmatism, distortion, curvature of image field, and chromatic aberration. Any departure from the upper limit would seriously aggravate these various aberrations and also greatly reduce the eye distance.

Condition (2) above is useful in that the lens surface R10 of the sixth element L6 is concaved toward a notshown objective lens (i.e., convexed toward the eye) to thereby under-correct the coma with respect to the light rays incident on the marginal area of the view field of the lens surface R10 so as to negate the over correction in the lens surfaces R3, R8, etc.; and further that the lens surface R9 of the sixth element L6 is concaved toward the eye, and together with the relation n n reduces the distortion in the focusing lens as well as providing a good correction of the lateral chromatic aberration. In addition to these advantages. condition (2) serves to locate the rear principal point of the entire system nearer to the eye to increase the eye distance. 1f the sixth element L6 in the present em-bodiment is a plano concave lens or a negative meniscus lens or extremely, if the fifth and sixth elements L5 and L6 are disposed in inverted order with the sixth element L6 comprising a biconvex lens, then the abovedescribed advantages of the present invention would be lost, thus failing to provide a wide angle eyepiece having such a long eye distance as could be provided by the present invention.

Condition (3) above is intended to provide a balance between the refractive power of the focusing lens group and that of the stationary lens group. Any value of the subtotal focal length j less than the value 0.7f would mean a relative increase in the subtotal focal length f, of the focusing lens group, and accordingly an excess in the adjustment of the visibility, i.e., the amount of displacement of this lens group per diopter, thus requiring a very great value for the distance d, between the stationary lens group and the focusing lens group. Also, in such a case, the refractive power of the focusing lens group would be reduced to give rise to the necessity for a greater diameter of the stationary lens group which, in turn, would result in a reduced eye distance and unsatisfactory correction of various aberrations, particularly coma and distortion, in the entire system.

Condition (4) above is directed to the correction of the chromatic aberration in the entire eyepiece. 1f the first element L1 is formed of a glass material whose dispersive power for light is lower than the limit prescribed by this condition, the various aberrations, particularly lateral chromatic aberration, in the focusing lens group would be under-corrected to fail in providing a good correction of the chromatic aberration in general.

An example of the internal focusing wide angle eyepiece which satisfies all the foregoing conditions will be shown below.

Example 1 Relative Aperture F/3.6', Angle of View 2 a 68 R1 5724.138

a 6.897 n 1.80518 0, 25.5 R2 218.138

d,=37.931 n,= 1.65160 v,= 58.5 R3 126.986

d, 1.379 R4 -l11046.9

d 24.138 '1: 1.62041 v 60.3 R5=232.759 (A) (B) (C) d, 55.172 31.034 6.897 R6 266.414

d, 20.690 I14 1.62041 II 603 R7 5551.724

d 58.621 n, 1.62041 11 60.3 R9 152.331

d,,=6.897 n,,= 1.80518 v 25.5 RIO 334.004

(B) (C) Total focal length f 104.8mm 100.0mm

95.6mm Back focus B.f. 4.3mm 16.9mm 28.5mm Angle of view 201 68 It should be understood that visibility is zero diopter when d; is of the value shown at (B).

Tables (A), (B) and (C) below show Seidel coefficients for negative, zero and positive diopter, respectively.

Lens Surfaces 1 11 111 IV V R 1 0.0000 0.0000 0.0078 0.0078 0.0001 R2 0.0165 0.0165 0.0731 0.0401 0.0154 R3 0.7782 0,7782 2.6452 1.0889 0.99l6 R4 0.0648 0.0648 0.1980 0.0683 0.1997 R5 06167 0.6167 2.0146 0.7812 l.0375 R6 0.0537 0.0537 0.0175 0.0900 0.2888 R7 0.1526 0.1526 0.4509 0.1457 0.5761 R8 0.0709 0.0709 0.0071 0.1347 0.3993 R9 0.0065 0.0065 0.0608 0.0479 0.0821 R10 0.0237 0,0237 0.0625 0. 1099 0.6488 2 1.3588 l.3588 4.6995 1.9821 2.2688

Total focal length f= 1.048

Stop is disposed 0.67l ahead of the lens surface Rl Lens Surfaces 1 11 111 IV V R1 0.0000 0.0000 0.0078 0.0078 0.0001 R2 0.0165 0.0165 0.0731 0.0401 0.0154 R3 0.7782 0.7782 2.6452 1.0889 0.9916 R4 0.0648 0.0648 0. 1980 0.0683 0.1997 R5 0.6167 0.6l67 2.0146 0.7812 1 .0375 R6 41.0516 0.0516 0.0110 0.0922 0.2607 R7 0.2383 0.2383 0.7081 0.2314 -0.7003 R8 0.0827 0.0827 0.0425 0.1229 0.4033 R9 0.0300 0.0300 0.1316 0.0715 0.1305 R10 0.1038 +0.1038 0.1778 0.0298 0.7714 1 1.4914 l.49l4 5.0973 2.1147 2.49l3

Total focal length f- 10 Stop is positioned 0.690 ahead of the lens surface Lens Surfaces 1 11 111 IV V Rl 0.0000 0.0000 0.0078 0.0078 0.0001 R2 0.0l65 0.0165 -0.073l 0.0401 0.0154 R3 0.7782 0.7782 2.6452 1.0889 0.99l6 R4 -0.0648 0.0648 -0. 1980 0.0683 0.1997 R5 0.6167 0.6l67 2.0146 0.7812 -l.0375 R6 0.0446 0.0446 0.0098 0.0991 0.2267 R7 0.3427 -0.3427 1.0211 0.3358 O.8448 R8 -0.0875 0.0875 0.0568 0.1181 0.3965 R9 0.0775 0.0775 0.2741 0.ll90 0.2058 R10 0.1916 O.l9l6 0.4414 0.0581 0.9023 2 1.6383 1.6383 5.5379 2.2616 2.7322

Total focal length f= 0.956 Stop is positioned 0.707 ahead of the lens surface As the result of the realization of such an internal focusing wide angle eyepiece, it is possible to provide a device whose bodytube is invariable in its apparent length irrespective of any adjustment effected on the visibility or on the focal point by means of the eyepiece, and this leads to the feasibility of increasing the strength and rigidity of the eyepiece portion of the device which has heretofore been fragile. Moreover, the construction of the present invention in which only the inner lens group is movable, instead of the entire eyepiece as in the prior art, permits the whole bodytube to be much more readly maintained airtight and waterproof by fixing the outer stationary lens group completely immovably and intimately to a bodytube supporting frame. Furthermore, even if the focusing group is moved to vary the visibility or the focal point, the various aberrations very well corrected over a wide angle of view exceeding 68 may be substantially invariable, thus providing an internal focusing wide angle eyepiece comprising six elements and permitting a very long eye distance.

Such an internal focusing eyepiece may also be used as an excellent eyepiece of the convention type, not of the internal focusing type, by fixing the stationary lens group and the focusing lens group with a certain spacing therebetween maintained in the range of'O d 1. If, i.e., by maintaining the distance d constant, so as to permit movement of the entire eyepiece system.

Referring now to FIG. 3(A), there is shown another embodiment of the internal focusing wide angle eyepiece according to the present invention, which again comprises six lens elements. As viewed from left to right in the figure, the eyepiece includes a first element Ll such as a negative meniscus lens convexed toward the eye or a plane-convex lens flattened toward the eye, a second element L2 such as a biconvex lens, a third element L3 such as a positive meniscus lens concaved toward the eye, a fourth element L4 such as a positive meniscus lens convexed toward the eye, a fifth element L5 such as a biconvex lens, and a sixth element L6 such as a biconcave lens. F is a focal plane of the entire eyepiece and B.F. is back focus. the first and second elements L1 and L2 and the fifth and sixth elements L5 and L6 are cemented together, respectively. When the visibility is zero diopter, it is assumed that the total focal length of the entire eyepiece isf, the subtotal focal length of the first and second elements L1 and L2 isf the subtotal focal length of the third to sixth elements isf the radii of curvature of the successive lens surfaces are R1, R2, etc., the center thicknesses or the interspatial distances of the successive elements are d,, d,, etc., the refractive indices of the respective elements for the light having a wavelength of 5876A are m, n,, etc., and the Abbe numbers of the successive elements are 11,, v etc. Then the shown arrangement satisfies the following conditions:

I. With the lens group of the first and second elements L1 and L2 stationary and with the focusing lens group of the third to sixth elements axially movable together within the range of 0 d 5 0.9f, adjustment of the visibility can be made between negative, zero and positive degrees and focusing can be effected between the infinite and the closest distance.

2. The sixth element L6 is a biconcave lens with a refractive index n 5 n 3. f, a f.

As regards the condition (1 above, it is natural with a wide angle eyepiece of the internal focusing type that the outer lens group thereof, i.e., the first and second elements adjacent the eye should be stationary while the inner lens group should be movable. According to the present embodiment, the inner lens group, comprising the third to sixth elements which are movable together, provides a focusing lens.

The upper limit 0 0.9f of the condition that 05 d 5 0.9f is the limit of the negative visibility (FlG. 3A), and the lower limit d 0, i.e., the limit at which the third element L3 of the focusing lens contacts the second element L2, is the limit of the positive visibility (FIG. 3C). Between these two limits, the focusing lens may be freely moved and together with the conditions (2) to (4), this maintains good conditions of various aberrations such as spherical aberration, coma, astigmatism, distortion, curvature of image field, and chromatic aberration. Any departure from the upper limit would seriously aggravate these various aberrations and also greatly reduce the eye distance.

Condition (2) above is useful in that the lens surface R10 of the sixth element L6 is concaved toward a notshown objective lens (i.e., convexed toward the eye) to thereby under-correct the coma therein with respect to the light rays incident on the marginal area of the view field of the lens surface R10 so as to negate the overcorrection in the lens surfaces R3, R8, etc., and further that the lens surface R9 of the sixth element L6 is concaved toward the eye and together with the relation n 5 n this reduces the distortion in the focusing lens as well as provides a good correction of the lateral chromatic aberration. In addition to these advantages, the condition (2) serves to make the rear principal point of the entire system nearer to the eye to increase the eye distance. If the sixth element L6 in the present embodiment is a plane-concave lens or a negative meniscus lens, or extremely, if the fifth and sixth elements L5 and L6 are disposed in inverted order with the sixth element L6 comprising a biconvex lens, then the above-described advantages of the present invention would be lost, thus failing to provide a wide angle eyepiece having such a long eye distance as could be provided by the present invention.

Condition (3) above is intended to provide a balance between the refractive power of the focusing lens group and that of the stationary lens group. Any value of the subtotal focal length f, of the first and second elements L1 and L2 less than the prescribed range would mean a relative increase in the subtotal focal length f: of the focusing lens group, and accordingly an excess in the adjustment of the visibility, i.e., the amount of displacement of this lens group per diopter, thus requiring a very great value for the distance d between the stationary lens group and the focusing lens group. Also, in such a case, the refractive power of the focusing lens group wouldbe reduced to give rise to the necessity for a greater diameter of the stationary lens group which, in turn, would result in a reduced eye distance and unsatisfactory correction of various aberrations, particularly coma, astigmatism and distortion, in the entire system.

Condition (4) above is directed to the correction of the chromatic aberration in the entire eyepiece. 1f the first element L1 is formed ofa glass material whose dispersive power for light is lower than the limit prescribed by this condition, the various aberrations, particularly lateral chromatic aberration, in the focusing lens group would be under-corrected to fail in providing a good correction of the chromatic aberration in general.

An example of the internal focusing wide angle eyepiece which satisfies all the foregoing conditions will be shown below.

Example 2 Relative aperture F/3.6; Angle of view 204 68 R1 6424.828

Total focal length f Back focus B.f. Angle of view 201 68 104.7mm 100mm 95.7mm 20.9mm 25.0mm- 28.8mm

It should be understood that visibility is zero diopter when 81;, is of the value shown at (B).

Tables (A), (B) and (C) below show Seidel coefficients for negative, zero and positive diopter, respectively.

Lens Surfaces l 11 111 1V V R1 0.0000 0.0000 0.0069 0.0069 0.0000 R2 0.01 16 0.0116 0.0559 0.0327 0.0108 R3 0.8343 0.8343 2.8193 1.1507 1.0621 R4 "0.0571 0.0571 0.1748 -0.0606 0.2004 R5 0.3580 0.3580 1.2384 0.5224 0.7235 R6 0.0404 0.0404 0.0225 0.1033 0.2212 R7 0.2187 0.2187 0.6491 0.2118 0.6463 R8 0.0689 0.0689 0.0012 0.1367 0.3548 R9 0.0341 0.0341 0.1439 0.0756 0.1323

Total focal length f= 1.047

Stop is positioned 0.616 ahead of the lens surface R1.

Lens Surfaces l 11 111 IV V R1 0.0000 0.0000 0.0069 0.0069 0.0000 R2 0.01l6 0.0116 0.0559 0.0327 0.0108 R3 0.8343 0.8343 2.8193 1.1507 1.0621 R4 0.0631 0.0631 0.1928 0.0666 0.2065 R5 0.4645 -0.4645 1.5579 0.6290 0.8596 R6 0.0436 0.0436 0.0130 0.1001 0.2270 R7 0.2818 0.2818 0.8384 0.2749 0.7507

R8 0.0798 0.0798 0.0337 0.1258 0.3804 R9 0.0539 0.0539 0.2032 0.0954 0.1678 R10 0.1399 0.1399 0.2646 0.0153 0.7886 2 1.4685 1.4685 5.0145 2.0774 2.4685

Total focal length f= 1.0

Stop is positioned 0.669 ahead of the lens surface R1.

Lens Surfaces 1 11 111 1V V R 1 0.0000 0.0000 0.0069 0.0069 0.0000 R2 0.01 16 0.0116 0.0559 0.0327 0.0108 R3 0.8343 0.8343 2.8193 1.1507 1.0621 R4 00692 0.0692 0.21 10 *00727 0.2128 R5 0.5921 0.5921 1.9407 0.7565 1.0177 R6 -0.0465 0.0465 0.0043 0.0972 0.2322 R7 0.3565 0.3565 1.0627 0.3496 0.8688 R8 -0.0911 0.091 1 0.0676 0.1145 0.4064 R9 -0.0806 0.0806 0.2833 0.1221 0.2114

Total focal length f= 0.957

Stop is positioned 0.717 ahead of the lens surface Rl.

The internal focusing wide angle eyepiece as shown in Example 2 may also lead to the various advantages described previously with respect to Example 1. Further, such an internal focusing eyepiece may also be used as an excellent eyepiece of the conventional type, not of the internal focusing type, by fixing the stationary lens group and the focusing lens group with a certain spacing therebetween maintained in the range of 0 d; 0.9f, i.e., by maintaining the distance (1;,

constant, so as to permit movement of the entire eypepiece system.

We believe that the construction and application of our novel eyepiece will now be understood and that its advantages will be fully appreciated by those persons skilled in the art.

We claim:

1. A wide angle eyepiece for an internal focusing optical system ofa viewing instrument comprising, axially from rear to front,

a biconvex doublet eyelens having a negative meniscus element curved towards the eye and a biconvex element cemented to each other,

a first positive meniscus single lens concaved toward the eye,

a second positive meniscus single lens convexed toward the eye, and

a positive meniscus doublet field lens having, a biconvex element and a biconcave element cemented to each other,

said field lens and at least one of said single lenses being axially movable in unison for focusing.

2. A wide angle eyepiece according to claim 1,

wherein the following data is satisfied:

Relative aperture F/3.6; Angle of view 20: 68 R1 5724.138

d, 6.897 n, 1.80518 1 25.5 R2 218.138

d,=37.931 n,= 1.65160 v,=58.5 R3 -126.986

(A) (B) (C) R6 266.414 4, 55.172 31.034 6.897

d, 20.690 n. 1.62041 9, 60.3 R7 5551.724

d,= 6.897 n, 1.80518 9, 25.5 R10== 334.004

(A) (B) (C) Total focal length f 95.6mm Back focus 8.1.

- 104.8mm 100.0mm

- 4.3mm 16.9mm 28.5mm

3. A wide angle eyepiece according to claim 1,

wherein the following data is satisfied:

Relative aperture F/3.6; Angle of view 2a 68 d. 6.897 n 1.80518 R2 245.034

d,- 37.931 n,= 1.65160 R3 -124.69 (A) (B) (C) d; 41.379 24.138 6.897 R4 I 1 1046.9 d =24.138 n;,= 1.62041 R5 232.759

d, I 1.379 R6 266.414

d, I 1.379 R 8 186.207

Total focal length f Back focus B.f.

= 104.7mm mm 95.7mm 20.9mm 25.0mm 28.8 mm

Patent No, 3,768,890 Dated October 30, 1973 inventor) 'KYIYOYASUYOSAWA ET AL.

It is certified thaterror appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 28, before 'lwide", insert the Colunm 4, line 66, at E, 3rd vertical c o1umn,change "-5.0973" to 5.0973 I J v Columa 9 claim 3, cancel "d =24:l38" from vertical column 1. and insert same in vertical column 2 two lines below "Fd ..6897||.

Signed and sealed this Lpth day of June 197% (SEAL) Attesfi:

EDWARD M.F'LETCH ER,JR c. MARSHALDDANN Attesting Officer Commissioner of Patents FORM PO-105O (10-69) uscoMM-oc 9031mm; 

1. A wide angle eyepiece for an internal focusing optical system of a viewing instrument comprising, axially from rear to front, a biconvex doublet eyelens having a negative meniscus element curved towards the eye and a biconvex element cemented to each other, a first positive meniscus single lens concaved toward the eye, a second positive meniscus single lens convexed toward the eye, and a positive meniscus doublet field lens having, a biconvex element and a biconcave element cemented to each other, said field lens and at least one of said single lenses being axially movable in unison for focusing.
 2. A wide angle eyepiece according to claim 1, wherein the following data is satisfied: Relative aperture F/3.6; Angle of view 2 Alpha 68*R1 5724.138 d1 6.897 n1 1.80518 Nu 1 25.5 R2 218.138 d2 37.931 n2 1.65160 Nu 2 58.5 R3 -126.986 d3 1.379 R4 -11046.9 d4 24.138 n3 1.62041 Nu 3 60.3 R5 - 232.759 (A) (B) (C) R6 266.414 d5 55.172 - 31.034 - 6.897 d6 20.690 n4 1.62041 Nu 4 60.3 R7 5551.724 d7 1.379 R8 186.207 d8 58.621 n5 1.62041 Nu 5 60.3 R9 -152.331 d9 6.897 n6 1.80518 Nu 6 25.5 R10 334.004 (A) (B) (C) Total focal length f 104.8mm - 100.0mm - 95.6mm Back focus B.f. 4.3mm - 16.9mm - 28.5mm
 3. A wide angle eyepiece according to claim 1, wherein the following data is satisfied: Relative aperture F/3.6; Angle of view 2 Alpha 68*R1 6424.828 d1 6.897 n1 1.80518 Nu 1 25.5 R2 245.034 d2 37.931 n2 1.65160 Nu 2 58.5 R3 -124.69 (A) (B) (C) d3 41.379 - 24.138 - 6.897 R4 -11046.9 d4 24.138 n3 1.62041 Nu 3 60.3 R5 -232.759 d5 1.379 R6 266.414 d6 20.690 n4 1.62041 Nu 4 60.3 R7 5551.724 d7 1.379 R8 186.207 d8 58.621 n5 1.62041 Nu 5 60.3 R9 -152.331 d9 6.897 n6 1.80518 Nu 6 25.5 R10 287.323 (A) (B) (C) Total focal length f 104.7mm - 100mm -95.7mm Back focus B.f. 20.9mm - 25.0mm - 28.8 mm 